1. Field of Invention
This invention relates to apparatus for measuring the electrical characteristics of crystalline solids from which semiconductor wafers are fabricated for the transistor and integrated circuit industry, and more particularly to apparatus which measures the electrical resistivity in successive increments of as-produced semiconductor crystals.
2. Description of Prior Art
In the manfacture of semiconductor crystals from which semiconductor wafers are fabricated, there is a process termed crystal pulling which involves dipping a seed crystal into a semiconductor melt and then slowly withdrawing the seed crystal. The process of crystal pulling involves alloying extremely minute amounts of a selected impurity into a crystal to enable it to exhibit required conductivity or resistivity characteristics. An increase in impurity concentration decreases the electrical resistivity characteristic of the raw manufactured crystal. Apparatus utilized in manufacture of semiconductor crystals requires a very stable, both mechanically and thermally, apparatus having provisions for alloying impurities at a very constant rate.
Recent emphasis has been placed on the development of methods and apparatus for accurately and automatically measuring electrical resistivity characteristics of semiconductor crystals produced by the crystal pulling process so as to quality categorize the raw crystal material for subsequent manufacture of semiconductor devices.
Prior art apparatus utilized in measuring the electrical resistivity of as-produced semiconductor crystals, for the purpose of determining relative crystal purity, were completely manual in operation for fixturing the crystal specimen within the resistivity probe apparatus. Mechanical arrangement of the probe apparatus made it difficult to load and unload the crystal specimen for rapid electrical resistivity measurements. Non-precise resistivity measurements were caused by voltage sensing probes that could not conform to the outer surface of the as-produced crystal, when actuated perpendicular to the crystal longitudinal centerline. Nonuniform electric current fields were created in the vicinity of the electrical contactors, which interfaced with the crystal body, providing the electric current field necessary for the resistivity measurements. Error was introduced into resistivity measurements due to visible light induced effects and stray electrical RF signals. A limitation was also placed on the allowable geometrical size of the crystalline solid which could be accommodated with the resistivity probe apparatus.
Prior art apparatus proved to be undesirable from the standpoint of relative ease of loading the crystal specimen, electrical interface contactor design which did not provide a uniform electric field in the vicinity of these contactors and light and heat energy induced effects in the electrical resistivity measurements derived from the environment of the resistivity test apparatus.